The present invention relates generally to telescopic sights having a focus adjustment achieved by longitudinal movement of an erector lens unit relative to the objective lens and eyepiece lens within such sight, and in particular to such a telescopic sight apparatus with such a focus adjustment while maintaining substantially fixed magnification over a wide range of object viewing distances. The focus adjustment is achieved by rotating a knob about an axis of rotation which extends substantially perpendicular to the longitudinal movement of the erector lens unit and is coupled thereto by a pin which is offset from such axis of rotation so that it orbits about such axis. Thus, rotation of the focus adjustment knob causes longitudinal movement of a lens mounting tube within which the erector lenses are mounted. The telescopic sight apparatus of the present invention is especially useful for a riflescope.
It is known to provide a telescopic sight for a riflescope with a movable erector lens unit which is adjusted longitudinally in order to vary the power or magnification by rotation of a cam sleeve having slots therein which are coupled by cam follower elements to the erector lens mounting tube, as shown in U.S. Pat. No. 3,058,391 of Leupold issued Oct. 16, 1962; U.S. Pat. No. 3,161,716 of Burris et al, issued Dec. 15, 1964 and U.S. Pat. No. 3,213,539 of Burris issued Oct. 26, 1965. However, in none of these prior riflescopes is longitudinal movement of the erector lens unit employed for adjusting the focus of a constant magnification telescopic sight in the manner of the present invention. Furthermore, none of these prior telescopic sights have a focus adjustment control in the form of a knob which rotates about an axis of rotation that extends substantially perpendicular to the longitudinal movement of the erector lens unit and is coupled thereto by a coupling pin offset from the axis of rotation so that such pin orbits about such axis to provide longitudinal movement to the lens unit, in the manner of the present invention.
It has previously been proposed in U.S. Pat. No. 4,408,842 of Gibson issued Oct. 11, 1983, U.S. Pat. No. 3,297,389 of Gibson issued Jan. 10, 1967 and U.S. Pat. No. 4,247,161 of Unertl issued Jan. 27, 1981 to provide a telescopic sight as a riflescope in which the erector lens unit is mounted within a lens tube that is moved laterally at one end by pivoting about the other end thereof to provide elevation and windage adjustments. This is achieved by rotation of windage and elevation adjustment knobs which extend into engagement with the lens tube to laterally displace such lens tube from the longitudinal axis of the telescopic sight apparatus. However, unlike the present invention, there is no longitudinal adjustment of the lens tube by rotation of a knob about an axis of rotation perpendicular thereto to enable longitudinal movement of the erector lens for focusing adjustment in the manner of the present invention.
In addition, U.S. Pat. No. 2,997,916 of Friedman et al issued Aug. 29, 1961 discloses a telescopic sight for a riflescope having an axially adjustable eyepiece lens for primary focusing and having an erector lens unit mounted in a tube which is adjusted longitudinally to reduce reticle image parallax. In this sight the reticle and the eyepiece are both attached to the opposite ends of the mounting tube of the erector lens so that they move with the erector lens during rotation of the parallax adjustment ring. Thus, the erector lens is not adjusted longitudinally relative to the objective lens, the eyepiece lens and the reticle in the manner of the telescopic sight of the present invention. Furthermore, longitudinal adjustment of the mounting tube of the erector lens unit in such patent is not achieved by rotation of an adjustment knob about an axis of rotation extending substantially perpendicular to the longitudinal axis of adjustment of the erector lens. Also, the parallax adjustment ring is not coupled to the erector lens unit by a coupling pin offset from the axis of rotation so that it orbits about such axis to provide such longitudinal movement of the lens tube, in the manner of the present invention.
The focus adjustment by longitudinal movement of the erector lens unit in the manner of the present invention is much simpler and more accurate than the focus adjustment means of the above cited patents. In addition, the focus adjustment means of the present invention provides extremely accurate focus adjustment over a wide range of viewing distances while maintaining a substantially fixed magnification which varies less than about ten percent. Thus, the magnification of the erector lens unit varies less than one percent during focus adjustment over a viewing range of from infinity to 100 meters.